This invention relates in one aspect to blends of normally solid, adhesive thermoplastic resins with normally solid non-adhesive thermoplastic resins and to films and laminates made therefrom. In another aspect, the present invention relates to blends of low density polyethylene with copolymers of ethylene and relatively polar comonomers such as ethylenically unsaturated carboxylic acids or vinyl ester monomers and to films and laminates thereof. In yet another aspect, this invention relates to 3 or more component blends comprising
(1) a relatively high melt index adhesive thermoplastic resin,
(2) a relatively low melt index adhesive thermoplastic resin, and
(3) a relatively low melt index non-adhesive thermoplastic resin.
A variety of somewhat polar synthetic thermoplastic polymers such as random copolymers of ethylene with acrylic or methacrylic acid; ethylene/vinyl acetate copolymers; etc. are known to exhibit reasonably good adhesion to a variety of metallic and non-metallic substrates and to be useful, for example, in single layer (e.g., free film) form, or as one or more layers in multiple layer film structures, as adhesives, binders, coatings, backings and the like for metallic and non-metallic objects.
In the use of the aforementioned synthetic thermoplastic polymers, particularly in their use in the form of monolayer or multiple layer films thereof, a number of oftentimes competing or conflicting considerations or factors can become involved. For example, it is often desirable that the above-noted type of polymer films exhibit strong adhesion to the type of substrate to which it is to be applied and that such degree of adhesion be achievable at the least strenuous processing or lamination conditions as are practicable in a given instance (e.g., at the lowest practicable combination of lamination temperature and pressure). On the other hand, however, it is also generally desirable that such films do not adhere too firmly to themselves (a phenomenon generally referred to in the art as "blocking") when in roll form during the conditions encountered during the manufacture, storage, shipment or use thereof. This is particularly important since such films could otherwise become extremely difficult, or essentially impossible, to retrieve in undamaged free film from the rolls thereof in which they are conventionally placed for efficient storage, shipment and ultimate use. Accordingly, the development of polymer compositions for laminatable adhesive films having a suitable combination of properties (e.g., suitable physical properties such as tensile strength and elongation, processability on conventional extrusion and lamination equipment, along with the desired high degree of adhesion to various substrates while at the same time not adhering so strongly to itself while in roll form as to cause troublesome "blocking" problems) generally requires a very careful balance between such completing properties and considerations.
In view of the foregoing, it would be highly desirable to provide thermoplastic adhesive polymer compositions having good processing characteristics on conventional extrusion equipment to thereby provide films capable of developing a high degree of adhesion to various substrates while still exhibiting good non-blocking properties to itself when in roll form during the manufacture, storage, shipment and use thereof.